Natural hair color is derived from melanin granules embedded throughout the cortex of hair fibers. Two general classes of such pigments have been identified: eumelanins (brownish black) and pheomelanins (reddish orange). The combination ratio and concentration of these two types of pigments impart to the hair its characteristic natural gradations of color. Dark hair has a higher concentration of the eumelanins, while red hair has a predominance of the pheomelanins. Light blond hair has reduced amounts of both.
Human hair is arbitrarily assigned a scale of ten levels to describe its darkness (or lightness). Black hair is designated as level one, medium brown hair as level five, and pale light blond as level ten, with several nuances in between.
Hair bleaching is a chemical process by which the melanin pigment granules are gradually destroyed by the bleaching agent, resulting in lighter hair color. The melanin pigments are not all lightened at the same rate. The eumelanins are easier to break down than the pheomelanins. Because of this property, dark hair, when bleached, experiences preferential destruction of the melanin pigments, which leads to the visual enhancement of the red pigments, and the casting of an undesirable warm reddish orange or “brassy” tone to the bleached hair. In order to neutralize this warmth, hair colorants of a drabbing nature are almost always applied during or after a bleaching treatment.
Based on their chemical composition and their strength, hair bleaches may be classified into two groups, designated as Category-1 and Category-2.
Category-1 bleaches are liquid- or cream-based compositions utilizing alkaline hydrogen peroxide solutions as the main oxygen-generating agent to oxidize and bleach hair melanin, usually in conjunction with a hair coloring process. Just before use, the peroxide is mixed with an alkalizing agent such as ammonia, and the resulting liquid or cream is applied to hair for 30 to 60 minutes. Such compositions may lighten the hair by as much as four levels at the most, depending on the concentration of hydrogen peroxide used. For example, a level-6 hair may be lightened, under favorable conditions to a level 10.
Category-2 bleaches are generally powder compositions, some in cream form, which are based on persulfate salts (ammonium, potassium, sodium) as auxiliary or booster supplies of active oxygen, and silicate and/or carbonate salts as sources of alkalinity. Again, just before use, they are mixed with hydrogen peroxide solutions to form a workable cream that can be applied to the hair. It is even possible to have hydrogen peroxide itself incorporated into the powder bleach in a solid form, and all that is needed to achieve a workable cream is to add water to the powder. Quite often, a third separately-packaged component, referred to as a bleach oil, which may contain humectants and other conditioning agents, is added to the bleach powder and peroxide at time of use.
Category-2 bleaches can deliver over seven levels of lift, something which cannot be attained with category-1 bleaches. They are usually utilized whenever more than four levels of lift are desired, such as when lifting a level-5 hair, or darker, to a pale blond. Because of the underlying warm tones that are exposed at various levels of bleaching, a toning process to neutralize the warmth and give the hair a pleasant natural look generally accompanies hair lightening. The toning process itself is a rather delicate one. Toners fall into three hues: blue-green, blue and violet, generally known as drabbing or ashing hues. These hues, or combinations of, are required to neutralize the spectrum of undertones that are exposed during the lightening process. Light brown hair, for example, would expose yellow undertones upon bleaching. Therefore, according to the law of color, a violet-based toner would neutralize the yellowish hue to result in a platinum or silver blond shade. The concentration of the toner should be adjusted so that the lift is not masked by the deposition of color. Similarly, medium brown hair would reveal a significant amount of orange undertones, requiring a significant amount of a blue-based toner. Dark hair, when bleached, exhibits reddish-orange undertones requiring a bluish-green toner.
At other times it is desirable to deposit a bright color on the hair. However, because of the dark pigment in the hair, it is not possible to do that without first bleaching the hair to a lighter color. It is customary therefore to perform a two-step process where the hair is lightened in a first step with category-2 powder bleach, then tinted with a bright color in a second step.
Category-1 bleaches constitute most of what is known as oxidative permanent hair colorants. They contain oxidative dyes. Some may contain Direct, Disperse, Acid, or Basic dyes, or combinations thereof. The prevailing alkaline peroxide environment of this category of bleaches is mild enough to allow for the survival of several types of dyes. Therefore, the limited lightening of hair pigments and the deposition of color is a simultaneous process, which is completed in about an hour.
In category-2 bleaches, the medium is quite intolerant to most dyes. The combination of higher alkalinity and stronger oxidizing conditions, act synergistically to destroy these dyes within a short period of time. Unlike the abundance of colorants surviving category-1 bleaches, only very few dyes have been identified to date which are both, stable in powder bleaches, and capable at the same time of dyeing hair efficiently.
Dyes in general consist of aryl rings or conjugated structures that contain unsaturated chemical groups such as (>C═C<), (>C═N—), (>C═O), (—N═O), or (—N═N—) referred to as chromophores. Weakly basic groups such as (—OH) or (—NH2), called auxochromes, are often attached to the aryl rings and assist in intensifying the color generated by the chromophores. Most chemical groups added to an aryl ring can affect the way the ring may undergo electrophilic substitution. Groups that withdraw electrons are called deactivating groups because once attached to benzene they render the ring less reactive than, the unsubstituted benzene, while others that donate electrons are called activating because the ring they are attached to becomes more active than benzene. Activating groups include hydroxy (—OH), amino (—NH2, —NHR, —NR2), alkoxy groups (—OCH3, —OC2H5, etc.) and alkylaznide (—NHCOR). Deactivating groups include nitro (—NO2), cyano (—CN), carboxy (—COOH, —COOR), sulfonic (—SO3H), or halide (—F, —Cl, —Br, —I). Activating groups are ortho, para directors because they cause attack on the aryl ring to occur at positions ortho and para to them, while deactivating groups (with the exception of the halogens) are meta directors because chemical attack occurs at the meta position with respect to these groups.
Based on structure, dyes are classified into the following chemical classes: acridine, anthraquinone, azine, azo, cyanine, formazan, indamine, indigoid, nitro, oxazine, phthalocyanine, quinophthalone, stilbene, thiazine, thiazole, triarylmethane, and xanthene.
A triarylmethane dye is built around a basic skeleton where a central methane carbon atom, shown in the drawings as Structure 1, is linked to three aryl nuclei that may be substituted at the para position relative to the central methane carbon, with primary, secondary, or tertiary amino groups, or hydroxy groups, or combination of both. In Structure 1 of the accompanying single figure, X, Y and Z may all be terminal aryl systems, naphthyl systems or combination thereof. Based on this basic plan, triarylmethane dyes may be divided as follows: A) Triphenylmethane dyes, where X, Y and Z in Structure 1 are all aryl derivatives; B) Diphenylnaphthylmethane dyes, where one of X, Y or Z in Structure 1 is a naphthyl group and the remaining group are phenyl groups; and C) Dinaphthylphenylmethane dyes, where two of the rings in Structure 1 are naphthyl groups and the remaining group is a phenyl group.
In absence of any acidic groups on the aromatic rings, triarylmethane dyes are termed cationic or basic dyes. The presence of sulfonic acid groups confers acidic or anionic properties as well as water solubility. In all divisions of the triarylmethanes, some or all of the aryl nuclei are substituted in the para position to the central methane carbon with auxochromes x1, y1, or z1 such that x1, y1, or z1 are hydroxy, amino or both, as in Structure 2. If the auxochrome is an amino group, it may be a primary amino (—NH2), a secondary amino (—NHR1) or a tertiary amino (—NR2), where R1 and R2 may be identical or different, and either may be alkyl, alkoxy, carboxy, cyano, alkyl-cyano, halogen, phenyl, or naphthyl substituent.
Triphenylnethane dyes constitute the majority of the triarylmethane class of dyes. The chromophoric system of these dyes consists of resonance hybrids involving the central carbon atom, which is sp2 hybridized, and the para-amino- or para-hydroxy groups located on the aromatic rings attached to that carbon.
Triarylmethanes may be synthesized via several routes such as the aldehyde synthesis, the hydrol synthesis and the ketone synthesis. In the aldehyde method, different aldehydes may be reacted with suitable aromatic amines, phenols or naphthols to form various amino or hydroxy derivatives. In the hydrol and ketone methods, diaryl hydrols or diaryl ketones may be reacted with suitable aromatic amines or phenols to form a variety of these dyes. In the case of the phenolphthalein and sulfonephthalein dye derivatives, synthesis is achieved by condensing aromatic anhydrides including phthalic anhydride and sulfobenzoic acid cyclic anhydride derivatives with phenols or benzoic acid derivatives.
Based on their chemical constituents therefore, triarylmethane dyes may be classified into at least five subclasses.
The first such subclass comprises monoamino derivatives in which only one aromatic ring contains a para amino auxochrome. An example is Fuchsonimine hydrochloride, CAS# 84215-84-9, shown as Structure 3.
The second subclass comprises the diamino derivatives in which two aromatic rings contain a para amino group. An example is CI Basic Green 4, CI 42000, CAS# 569-64-2, shown as Structure 4.
The third subclass comprises the triamino derivatives of triphenylmethane in which all three aromatic rings contain a para amino auxochrome, an example of which is CI Basic Red 9, CI 42500, CAS# 569-61-9, shown as Structure 5.
The fourth subclass comprises aminohydroxy derivatives where para amino and para hydroxy groups are present on separate aromatic rings, an example of which is CI Mordant Violet 11, CI 43550, shown as Structure 6.
The fifth subclass comprises the hydroxy derivatives, where one or more para hydroxy groups are present on one or more aromatic rings. These include typical ionic members such as CI Mordant Blue 3, CI 43820, CAS# 3564-18-9, shown as Structure 7, as well as nonionic members. The nonionic members are pH-dependent lactone and sultone triphenylmethane derivatives. At lower pH, the dye is in the nonionic lactone or sultone form, which is colorless because the central carbon atom is unable to participate in any resonance structure. At alkaline pH the dye ionizes and undergoes lactone or sultone ring opening to produce a colored stabilized triphenylmethane ion. Members of this division include the phthaleins and sulfonphthaleins families. Phthaleins include phenolphthalein, CAS# 81-90-3, shown as Structure 8, and the sulfonphthaleins include phenol red, CAS# 143-74-8, shown as Structure 9.
Azo dyes are characterized by the presence of one or more azo (—N═N—) groups, which are generally associated with auxocluromes such as amino (—NH—) and hydroxy (—OH) groups as is the case with triarylmethane dyes. The first step in their synthesis is the formation of a diazonium ion or a diazo component, shown as Structure 10, by a diazotation coupling reaction in which a nitrosating agent attacks a benzenoid component such as an arylaminie or a heterocyclic amine in which the amino group is attached to a nitrogen- or sulfur-containing ring. Examples of heterocyclic diazo components include those derived from 2-aminobenzothiazoles and their substituents, shown as Structure 11, 2-amino-5-nitrothiazoles and their substituents (shown as structure 12), 3-aminobenzisothiazoles and their substituents (shown as Structure 13) and thiophenes and their substituents (shown as Structure 14). Because the diazo components are such powerful electrophiles they can readily attack compounds having nucleophilic centers, which are called coupling components, to form azo dyes. Such coupling components include other arylamines as well as phenols, naphthols and keto-enol compounds (acetoacetarylamides, pyridones, pyrazolones, aminopyrazoles). Some examples follow of various azo dyes formed by using different diazo and coupling components:    Structure 15 is an example of an azo dye (C.I. Basic Orange 2) formed by the union of an arylamine-diazo component and an arylamine-coupling agent.    Structure 16 is an example of an azo dye (FD&C Red #40) formed by the union of an arylamine-diazo component and a naphthol-coupling agent.    Structure 17 is an example of an azo dye (C.I. Disperse Blue 156) formed by the union of a benzothiazole diazo component (6-nitro-2-aminobenzothiazole) and an arylamine-coupling agent.    Structure 18 is an example of an azo dye formed by the union of a nitrothiazole diazo component (2-amino-5-nitrothiazole) and an arylamine-coupling agent.    Structure 19 is an example of an azo dye (C.I. Disperse Blue 148) formed by the union of a benzisothiazole diazo component (5-nitro-3-aminobenzisothiazole) and an arylamine-coupling agent, while Structure 20 is another azo dye formed by combining a thiophene diazo component and an arylamine-coupling component.
The thiazine class of dyes is based around a central chromophoric thiazine ring, which is part of a condensed three-ring system whose outer components may be benzene or naphthalene nuclei. Blue thiazine dyes are obtained when auxochromes are introduced meta to the sulfur atom. An example is Methylene Blue (C.I. Basic Blue 9, Structure 21).
Nitro dyes are characterized by the presence of one or more nitro groups conjugated with electron-donor substituents such as hydroxy or amino groups on benzenoid or naphthol rings. Nitro dyes yield mostly hues in the yellow and brown range. An example is 2-amino-5-nitrophenol (Structure 22).
In the present inventors' earlier U.S. Pat. No. 5,688,291, a single-step composition was disclosed, which utilized disperse azo and anthraquinone compounds in category-2 bleach, to simultaneously lighten the hair up to seven levels and deposit different colors. The present invention discloses compositions consisting of other classes of dyes, namely acid and basic colorants containing specific chemical constituents, which are more substantive to hair and deliver enhanced deposit and more vivid colors. These acid and basic colorants belong chemically to the azo, triarylmethane, thiazine, and nitro classes, and can be used in conjunction with a category-2 bleach to lighten hair up to seven levels and deposit bright colors in a single step. They all have the unique property of possessing deactivating or weakly activating groups positioned ortho and/or para to the chromophoric and/or auxochromic centers of the dye molecules.
U.S. Pat. No. 5,474,578, to Chan, issued Dec. 12, 1995, discloses a process for temporary erasable hair coloring. The process utilizes a composition comprising triarylmethane dyes, which are subsequently decolorized or “erased” by reacting them with alkaline hydrogen peroxide. While the patent teaches the use of triarylmetbane dyes in a manner completely opposite to the teachings of the invention disclosed herein, namely by taking advantage of their known instability to alkaline hydrogen peroxide (category-1 bleach), yet the patent teaches in examples 5–7 that some triarylrnethane dyes could not be decolorized by alkaline hydrogen peroxide. As stated above and as those skilled in the art may know, dyes that are stable in category-1 bleach are not necessarily stable in category-2 bleach. To prove the point, dyes specified in examples 5–7 of Chan '578 were tested in the stronger bleach system described below (category-2 bleach). They were all decolorized and found to be unstable.
U.S. Pat. No. 5,232,494, to Miller, issued Aug. 3, 1993, discloses a system consisting of two coloring compositions for inks in markers and the like comprising of a first erasable coloring composition containing polymethine and azo dyes that are decolorized by bleach, and a second coloring composition containing pigments and xanthine dyes that are resistant to chemical attack. Again, as those skilled in the art know, dyes do not behave the same on different substrates. Hair keratin fibers are dramatically different from cellulosic paper fibers. Also the bleach system used with the second coloring composition comprised of agents that are rarely used in the hair care industry to bleach hair, such agents include hydrogen sulfide, sodium hypochlorite, and the preferred agent being sodium sulfite. Hydrogen peroxide was also mentioned but within the confines of a category I bleach system. When the xanthene dyes Acid Red 52 and Acid Red 87, mentioned in Miller '494 to be highly resistant to chemical attack in the erasable ink system, were tested in the bleach system described below, they were found to be unstable.
The advantages of category-2 bleaches with built-in effective colorants are significant. First, a single-step product will significantly reduce the time of the hair lightening and coloring process, a feature that appeals to both, the client and the salon operator. Second, it reduces the chances of scalp irritation due to prolonged contact of the skin with reactive chemicals (alkalinity, peroxide, oxidation dyes) in traditional two-step applications. And third, the single-step application significantly reduces the damage to the hair because it eliminates the need for additional chemical treatments.